1. Field of the Invention
The present invention relates to a flexible wired circuit board for temperature measurement and, more particularly, to a flexible wired circuit board for temperature measurement used as a temperature sensor.
2. Description of the Prior Art
In general, a thermocouple used for an automotive engine control is disposed in the vicinity of fuel combustion chamber of an automotive engine, for calculating combustion time, angles of valve heads, a mixing ratio between air and fuel (an air-fuel ratio), etc.
The thermocouple is usually disposed at a front end of a wired circuit board and covered with a cover member formed of heat-resistant material to protect the thermocouple from high-temperature atmosphere around the engine, so as to prevent errors caused by thermal electromotive force generated from parts other than points of contact for measuring temperature.
A variety of control methods have been proposed for providing improved temperature measurement accuracy of the thermocouple (e.g. Japanese Laid-open (Unexamined) Patent Publication No. 2001-188547).
To take a more accurate measurement of the temperature of the fuel combustion chamber of the engine by using the thermocouple, it is necessary that the thermocouple is positioned to be as close to the fuel combustion chamber as possible. However, since a conductive pattern of the wired circuit board is formed from copper foil, the conductive pattern, when used in a high-temperature atmosphere, changes in crystal structure, resulting in failure of a proportional relation of specific electric resistance of the conductive pattern to temperature. The changes in electric resistance cause errors in measured temperature. Due to this, the thermocouple is obliged to be spaced apart at a certain distance from the fuel combustion chamber of the engine, so that it is unavoidable that the temperature measurement accuracy of the thermocouple is reduced to that extent.
On the other hand, the temperature measurement accuracy of the thermocouple may be improved by use of a control, as mentioned above, but there is a limit to the improvement of the temperature measurement accuracy of the thermocouple by use of the control.
Further, covering the thermocouple with the cover member as mentioned above causes increase in manufacturing cost by the provision of the cover member.